I've played through ToEE (unmmodded aside from Co8 bugfixes) myself, and it's pretty good. It's a very faithful adaptation of the 3rd edition core ruleset. It's not a perfect implementation, but it's pretty darn close. This is both good and bad. Good in that 3rd edition combat is pretty solid after the first few levels, especially with a computer taking care of a lot of the more tedious elements. Bad in that 3rd edition still has plenty of flaws to it, especially in the first few levels, and the limited scope of core rules only keeps out the expanded material that worked to ameliorate them somewhat.
The campaign is pretty good for a dungeon crawl, with multiple paths and endings, although the combat encounters are a little uninspired, a product of the module's origins and age. This leads to a lot of large, sloggy fights towards the mid levels, where you're up against large numbers of fighter-type monsters that don't actually pose much of a threat individually and mostly serve as meat shields and speed bumps. Loot is also a little inconsistent, so having a couple of crafting feats on your spellcasters really helps. Overall, though, it really is a good, oldschool dungeon crawl.