Well, I'm playing in a 1e game, so I don't have to miss the good stuff - yay!
If I weren't in a 1e game, though, I would miss:
- Multi/class and dual-classing limits - 3 classes per character are MORE than enough!
- Varying XP advancement tables for different classes
- Race/class limits - dwarves shouldn't cast m-u spells, damn it!
- Being able to make a character without wading through heaps of feats, skills, blah blah blah
- No wealth/level guidelines
- Not being able to just run down the street to buy magic items
- Lots of other things