Oldish post, and now that 0.9.9.2 has come out, a few things may have changed a bit........
1: Ammo-chain. It's overpowered in it's synergy. It's too customizable. With 1 level of experience offset (for Juggler) it's too easy to overcome any situation without thought. Now with advanced assemblies it's even better. The only problem is........ it's friggin fantastic. In any game of DoomRL you never know what you're going to get. With Ammochain you do. You get a good (great) gun that doesn't need ammo. You get more backpack space because you can usually use all your mods straight away. You almost always get through the first few levels, even on N!, just because of shotgun juggling. It's just nice to know, you'll always be armed, always dish out damage, and will usually have some pretty spiffy armour to back you up. This just gets better with assemblies in the new version.
2: AotD. Shotguns, what's not to like? Area effect, no item destruction, corner shooting shotguns. And armour piercing shotguns at that. While some of the build seems a little redundant once you have it (Reloaderx2) the beauty of a power modded shotty is amazing. Any power modded shotty. You get good armour, never have to worry about just when to grab health, and a single/double/combat-barrel full of kick-arse. I haven't gotten around to trying out the new elephant gun, but it just makes this build even more beautiful. BOOM-click-click...........
3: Vampyre. It gets you SO many badges. It gets you SO many ranks. It changes the way you play the game. Running is a way of life, doors and spare green armour your friend. It's a totally different game, and it teaches you how to play the game with any other build, safely. Between being berserk most of the time, having good armour anyway, regen'ing health as you kill, doing sweet H2H damage and allowing you to have all this while still firing bullets is amazing. On AoB it's great. On just a normal game it kind of makes it a cake-walk sometimes. With one question, do you want to gun or do you want to run. And kill, Kill, KILL!!!!
For 0.9.9.2 I can see a few real standouts though. They've been considered a bit weaker up until now, and you now need to hope for mods (new Chained Courts runs essential), but Blademaster and Fireangle should be all the more powerful now. For two reasons. Tactical armour and boots. 40% faster regen'ing armour, with nice anti-knockback. How fast are you running/dodging? That's fast.
Of course, Vampyre might go a bit spastic with the chainsaw/mods/tactical armour or chainsword thing from the Chained Court in any case. What Arena Master??????