The new enemies are decidedly annoying, counter-intuitive and NO-FUN. They just gang up, deal unavoidable damage, and that's it. The previous enemies at least follow simple and predictable rules. The zone 4 guys don't.
The graphics is totally wrong too. You can't easily tell apart walls of different dig-levels. The enemies follow a completely different color theme (no more white-yellow-black, no more color-coded HP). Everything just looks completely random and counter-intuitive.