I'm surprised to hear this. I've played several thief-ish characters and always had a lot of fun. Granted, I don't think I ever completed the entire game with any of them. Honestly, it just isn't fun shooting your way through the BMC as a thief. Generally my thief characters came to an end after I'd visited all of the major cities. I think only ever went for the magickal route once. Other than that I've always found tech to be a bit better. Some points in mechanical can go a long way. Bear traps are useful for getting backstabs and as a way to immobilize bothersome guards. It might even be worth it to put points into explosives for stun grenades, or even to go further get points in chemistry. Knockout gas or paralysis grenades might be useful in a pinch. Of-course that would be a pretty big investment.