And that's what Flame Javelin is, that dichotomy; on the one hand, it isn't anything we haven't seen before... On the other hand, how can you possibly look away?
No, no. There's nothing to see here. Function, black, white; held strictly, there is absolutely nothing special whatsoever about Flame Javelin. A 4-damage instant spell in red for (functionally) three mana? That's good and all, but it's nothing that we haven't seen in one way, shape, or form elsewhere. And yet... Flame Javelin is anything but safe.
4 damage to the enemy's face? Flame Javelin as a three-mana nugget-smashing weapon is probably worse than both Flames of the Blood Hand (which can skillfully outmaneuver a Loxodon Hierarch for "8") and Pulse of the Forge (which has a kind of built-in card advantage). Good, sure, but...
So why can't we look away?
Flame Javelin doesn't just deal 4 damage to the opponent's face. That's all well and good—the red equivalent of a two-for-one to start—but Flame Javelin has that brutal versatility reminiscent of Char. The thing about Char, though, is that as good as that card was (and it was a persistent four-of in most aggressive red decks when it was legal in Standard), it always had those 2 points of collateral damage attached. You could never forget about those. I remember playing Gruul a couple of years back and being depressed that I had to side out my Chars against Boros because they were so bad in a race.
Flame Javelin doesn't have that particular problem. You pay three mana, you get 4 damage at instant speed. You can go after the opponent for the final 4, or you can knock a Wilt-Leaf Liege out of the way in almost leisurely fashion so you can get in with your pair of Tattermunge Maniacs. In this card we see the best of red deck flexibility...
...And, on three mana, no flexibility at all. The thing that is a little complicated is that cost on the most attractive casting of Flame Javelin. That's another reason why Flame Javelin is so intriguing, even though at first blush it might seem to be "just" a variation on cards we have seen before. Tournament Spikes want a fast, relatively inexpensive, yet high impact, card with which to finish opponents off and move along Wilt-Leaf Lieges... How did the mad geniuses in R&D accomplish that without unduly rocking the smooth sailing ship of game balance? They made the mana a little rough... but not too rough. For certain Flame Javelin as a three-mana option is going to reward the dedicated red deck. Yet... this is the set of Sunken Ruins,the realization (we assume) of the Graven Cairns cycle; in this world, where (again, we assume) there are dual lands capable of lapping Savannah and Taiga in terms of color fixing flexibility, Flame Javelin for three shouldn't really be really that hard to accomplish, even in a polychromatic deck.
So what if you don't have quite available? Like Beseech the Queen, Flame Javelin showcases the innovative new monocolor hybrid mana costs. With cards like Fulminator Mage and Demigod of Revenge in the format, don't be surprised if you have a stray Swamp or Urborg, Tomb of Yawgmoth... and not exactly even on turn four, even with your fourteen or so red sources. But that's okay! You can play Flame Javelin for .
I know that with all this talk of three-mana burn spells that might not be exactly what you were looking for, but believe me, four mana for this effect is not actually that bad a deal. Sure, it might seem a little unexciting just because of the awesome potential of the same card for three mana, but compare it to onetime defining burn spell Violent Eruption.
Think about this next to Bitterblossom (is Bitterblossom the new Tarmogoyf?). Yes, Bitterblossom is probably most effective in a Faeries deck with Scion of Oona to boost the team at trick speed and Mistbind Clique to upgrade a 1/1 or warp away the Bitterblossom itself should your life total start to wane... but it seems to be awesome everywhere, from Elves to Greater Gargadon theme decks. In the same way, Flame Javelin will be easiest to play the "redder" a red deck is, but it will probably be a reasonable inclusion in many different kinds of decks, including straight red, black-red, green-red, and blue-white.
I actually think that Flame Javelin for is pretty terrible for Constructed play. It's just not the kind of effect where a serious deck designer would typically spend difficult mana tuning (at least in most formats)... If a, say, blue-white player were interested in splashing an efficient burn spell utilizing one red mana, he might be much better off with Lightning Helix, Volcanic Hammer, or Incinerate, depending on the environment.
However, for no red mana at all, we have a very different situation entirely. Flame Javelin isn't even a splash at that point, but a multi-purpose tool not unlike a Triskelion that can be played by any deck (but for serious Constructed, with rare exception, the decks that would both want the effect on six and have the disposable mana to play it there would typically be blue-white). Unconsidered as it may be obvious, Flame Javelin in a completely off-color combination is like a sponge for metagame value, the kind of thing that can be heralded as genius by one mouth even as it is decried by awful from another side of the same room. A "safe" choice? Never. Interesting? Infinitely.
As a full-cost six-mana spell, Flame Javelin is probably most comparable to Mouth of Ronom.
On the other hand, at least the first time you play it, Flame Javelin showing only Nimbus Maze, basic Island, and the like will be a complete surprise. You can play it at the exact same times you can use a Mouth of Ronom (barring that enemy Teferi, Mage of Zhalfir being in play), but you may be able to take advantage of a considerable information imbalance.
Perhaps most importantly for a control deck in control-on-control situations (or any situation, depending on how mana-hungry the control deck is), unlike Mouth of Ronom, Flame Javelin doesn't gobble up a land when you use it. Blue mirrors are often about who has more lands in play, and setting yourself back one might be necessary... but also might not be the best as the game continues to develop into those grinding middle turns.
There are additional reasons why control decks might want a burn spell. For his innovative Korlash deck from Regionals 2007, I suggested that my friend Pat Chapin add Volcanic Hammer to bolster his Last Gasp count and help fight little beatdown decks; unsurprisingly, they were great for him. My friend Paul Jordan played the Innovator's Korlash deck and found himself up against a time crush against a Red Deck late in the Swiss. Gleefully he found the Volcanic Hammer he had sided in to deal with turn-two Scab-Clan Maulers... That Hammer of Bogardan was just as good as a nail in the coffin in the damage race. More expensive but also more flexible in these kinds of situations, Flame Javelin will doubtlessly Voltron together with base-5 damage sources like Oona, Queen of the Fae and one or so opposing uses of a Llanowar Wastes to Time Walk to the end of the game just one turn faster.
Even more pertinent in terms of the top of the deck and direct mana costs is this card up against Counterbalance. Mono-Red Burn and various Counterbalance Control, Point and Clique, and Next Level Blue decks were some of the most successful strategies of the recent PTQ and Grand Prix Extended format. Mono-Red Burn is going to grab up Flame Javelin and happily play it on three or four. Previously they could be trumped by an errant Threads of Disloyalty, Vedalken Shackles, or Thirst for Knowledge... There isn't much chance of Counterbalance / Sensei's Divining Top taking out Flame Javelin for free.
I think that you will agree that, in the spirit of monster movies and disaster flicks, it is time to move along, that there is nothing whatsoever interesting to see here... but you might want to scroll back up and take one last look at what will undoubtedly be a dominating red deck tool and surprising inclusion off-color across the color pie, because Flame Javelin is about to leave the building (and jump into your binder).