Yeah, re-reading some of the books here, I am seeing a lot of overlap. A lot of cross-compatability too. It's not inconcivable for a fighter to take the Squire kit from the Complete Paladin's for example. It's actually one of the things I quite liked about the kits. They added some flavor to a class, without (for the most part) unbalancing things too much.
That's why I pointed out Skills & Powers, its chapter on kits presents them for multiple classes, plus if you're using the NWP system in the book, NWPs that are parts of your kit cost one less CP to take, which adds another good benefit to using them. One of my late 2e projects was to take all the kits in the splats and stuff and set them up for use with PO. That got dropped with my compiled PO NWP list when I switched to 3e though.
You'll have to pick and choose, but then again "game balance" is a 3e concept.
Yet, there was a good deal of complaint in the Forum in Dragon back in the 2e days about balance, and I suspect there were online discussions as well.
Tome of Magic also introduces lots of new spells and items, and even the epic-level spells for priests.
I did say that ToM is practically core anyway, since a lot of people seemed to have it and it was frequently referenced. Also, it stayed in print over much of 2e's life, so it was probably in demand.
So, someone LIKED Player's Option then?
The PO line can be broken into two parts: New Systems and Tweaks. The New Systems, overall, were failures (CPs were too easy to abuse, the new initiative system was confusing, and the spell point system was just a lot of work). The Tweaks, however, were godsends. (New combat skills, a finally usable martial arts system, simple subraces and kits, a second stab at psionics, rebalanced spheres of magic and new specialists/divine casters all were amazing additions). Its also neat to see some of the proto-3e thinking going on in there.
Granted, I don't play 2e any more, but if I did, I'd make some of PO's changes mandatory.
PO wasn't that bad, but running it straight from the book isn't necessarily a good idea. It was presented as a collection of options anyway, so picking and choosing isn't bad. The DM does need to tweak things, particularly in Skills and Powers, if you want to it work well.
If Imperialus wants to use PO, I have one thing to say:
DON'T USE SUBABILITIES. Thanael can say what he wants about balance being new school, but subabilities are so broken that they can be horribly abused, and there was a lot said in Dragon about this. The worst case is the ugly Muscle/Stamina subs for Str where a character with a 17 Str can pump Muscle to 19 giving a huge bonus to hit and damage by skipping the entire Exceptional Str section on the tables all while lowering encumbrance a little. Dex and Int are pretty bad too IIRC, but Str is by far the worst offender.
Custom building character races and classes isn't too bad, but the DM needs to make sure there are limits in place so the system works well. There's a lot of abuse potential in using CPs, and I suspect they're flaws that weren't really intended.
There are some good things to be had in PO though. The proficiency system is better than the original. The new caster classes in S&M are pretty good. The psionics rules are easier to use. Probably if I went back to 2e, I'd continue using the PO NWP rules, and tinker with the CP system to make it more like a proto-3e. In particular, I'd use PO weapon proficiencies similar to feats.