Ethereum 2 is very different. It is proof of stake (PoS). This reuses the proof of work of Bitcoin (so very different properties for how hard it is to change blockchain history). Also, PoS has some bootstrapping issues where a new node cannot independently (without trusting other nodes) verify the history of blockchains.

Scalability properties are also very different. Eth2 tried the concepts of sharding between <pick a number> chains. That has issues around added complexity between the shards and contracts needing to execute on shards where other data/logic they need is already available (so gravitational pull towards a mega shard). Stacks has no shards and scales horizontally. FWIW, Eth2 seems to be doing a slow move away from the sharding concept towards layer-2 like scalability as well. They disabled code execution for shards and using them more for data availability in latest iterations.