I thought most of the thief's HLA's weren't really worth it (things like 'avoid death' etc are too specific and short-lived). Use Any Item allows the thief to not only wear cool armour but also to use scrolls like "stoneskin" and "timestop" (though there are still a few enemies who can't be time-stopped). Assassinate is worth it if you combine it with the short-sword of the mask +4/5 and improved haste (maybe even dual-wield with the short-sword of backstabbing). There are a couple of items that grant improved haste once or twice a day. Even if you only get a couple of hits in, it's better than a single backstab.

Common enemies can still be backstabbed - just not the big bosses/demons or annoying enemies who see through even cloaks of non-detection.
Spike trap is perhaps overly powerful - picked up a few of those in HLAs because the other HLAs didn't seem worth it. It's a bit cheap but laying a few spike-traps then running away so the enemy chases onto them (boots of speed help) can take out a few guys.
Dragons are the big problem for me - mostly I used vicky/edwin to summon a celestial with globe-of-blades to stand next to them (Deva at least seemed immune to buffeted wing attack)

It helped that the rest of my team were up to scratch (Korgan had so many greater-whirlwinds by the end that he could spam them through every big battle).

Consider the helm that casts simulacrum and you could have 2 assassins with assassinate and improved haste (I didn't try that as Korgan had that helm but UAE allows scrolls of simulacrum to be used too (though those are in limited supply)).

If you're playing through BG1 too then a fighter for a few levels then dualled to thief (and shadowkeeper to give it the assassin kit) might help (depends on how you feel about modding - personally I don't mind that kind of thing if it makes it more fun).
For a pure assassin though I'd still just go with putting points in short-sword and sword+shield / dual-wield, assassinate, UAE and spike-trap.

Bard class maybe is fogotten, but in my opinion it's one of the best. Maybe not for 6 characters team, but for smaller (like 2, 3 or 4 heroes groups) Bard is a beast. I think you can feel the power of Bards if you play in BG with only one hero. I played at BG 1 as a single bard and it was really fun! :-)

Bards Rulez!

I like bards, but I always felt that the BG games did not take full advantage of them. Unlike IWD1 in particular.

I love the whole Paladin, good v evil play of my 1st time round, just refound the game, thanks GOG, and am now playing through as a fallen cleric, very interesting. One of my fave char was the mesmer ni guild wars and also the dual wield thief, (ninja) in NWNS.