I've been playing competitive pokemon for about two years, and no, your team isn't going to be winning any prizes. First off, every one of your moves is offensive in nature. You don't have a single support move (except defog, which doesn't even count). Most good teams have about 1/4 support moves, and stall teams can easily have 2/3 support moves. Try adding some stat boosting moves on sweepers, and please put stealth rocks on at least one pokemon.
Secondly, both quake/edge and bolt/beam have neutral coverage on you team, which is a very bad thing., as it means offensive mons (i.e. Terrakion or Thundurus) could boost up and easily tear through your team. Also, both Typhlosion and Staraptor are weak to SR, which isn't a big problem in itself as both are offensive, but will prove to be troubling against dedicated teams.
My third complaint is about the movesets themselves. I'll go in order here:
Giratina is actually pretty good, except for slash, which should be replaced with WoW or roar or something.
Typhlosion should either run an entirely special set with choice specs (the power of specs eruption is terrifying) or go choice scarf, as your team needs a revenge killer.
Stararaptor should run brave bird for it's primary flying STAB, and double edge for its normal STAB. Keep close combat. You should either go band or scarf here (band if typhlosion is scarfed and visa versa), and replace defog with either quick attack (on band set) or U-turn (on choice set)
Alakazam should probably run focus blast instead of psybeam (to kill dark types) but is otherwise okay. Life orb is a good item choice, as it gives alakazam the versatility it needs (and the recoil doesn't matter much since almost everything OHKOs Zam anyway)
Empoleon looks like the best option to implement some hazard support. Try stealth rocks / scald / ice beam / toxic or grass knot or something. And give him left overs.
And as for your last slot, Gastrodon will help patch several defensive holes while choice band Terrakion will smash stuff up. It's pretty rounded as is, so pretty much anything will do.
Sorry for unnescasary criticism, I'm just in a grumpy mood today... :(