Introduction
Doom was top tier 1 year after the game was out, no longer top tier, Doom still has tools that are still very useful. Some people will say he's only useful for his Anti Air Assist, which is a very good assist, but he's much better than that.
Doom's main game is going to be zoning and keep away, you can rushdown with Doom, but lets face it, he's got a slow metal ass. You can mix it up to great effect, however.
Zoning with Pink Photons in the air is one of Doom's top tools. His gun (j.hp) is useful as well, his air Super Photons is a great super to use randomly, and if you get a lucker launcher, you can use it in a air series, a slow dialed LK, LK, XX super is probably your best bet.
He's also used for his amazing assist, his AAA is rocks, and they go everywhere, and pin, and chip. This is used in the Strider/Doom trap.
Moves List
Normal Moves
Special Moves
Super Moves
Assist Moves
Alpha
Expansion: Photon Shot
Good against jumpers and flyers and regain air control. Decent assist.
Beta
Anti-Air: Molecular Shield
As I said before, this assist will do a lot things for you.It's ONE OF the best assist in the whole game. You get free damage on superjumpers. When they jump in on you, call out Doom AAA and dash beneath to the other side. Always pick and abuse this assist.
Gamma
Projectile: Plasma Beam
The worst of Doom's assists. Don't bother picking this one.
The Basics
As stated above, Doom is best used on point as a keepaway character because he is too slow to really rushdown. The j.hp is useful to down Storm from a hailstorm and every now and then to take out Sentinel in the air, if you couple a j.hp with Sentinels drone assist, you get a mini trap that builds meter.
Also, Doom has a very good wavedash that can close the gap on his opponents very quickly. Doom's normal dash covers a lot of space, but his wavedash (df+pp) is leap after leap, covering full screen rather fast.
His top priority moves are his standing and crouching hp, and his df RH (launcher). One of Doom's guardbreaks is j.lp, land, df RH ^ AC of choice. Use his df RH on opponents who are jumping in on you due to its high priority, i'm not entirely sure if it has the same priority as Cyclops' df RH but I can't imagine it having more.
As an assist, Doom's rocks cover space and provide good chip, but as an AA it is not really as useful in the AA sense as Clops or Commando, I think of it as a psuedo drones assist. Also, it counters Commando but loses to higher priority assists like Psy AA, Clops AA etc., and beam assists like Cable proj or IM proj.
Also, his Photon Array Super (HCB PP) has instant start up in the air and does great chip damage. His other supers should be disregarded because they have no practical use and leave Doom open for retaliation.
Doom also has an unblockable, two guard breaks, and an infinite but that should be covered in the appropriate section (the advanced section). So curse Richards and enjoy playing Doom!