As a huge fan of the Styx games...
Pass on the first. Jump right to the second.
The first game was fun, but it had a lot of rough edges (lots of bottlenecks, etc), and a final segment that doesn't really fit the rest of the game and is nearly impossible without a ton of resources (and the super tough final level requires a lot of resources to pull off).
The second game fixes everything and improves the hell out of it. There are very few actual level design bottlenecks, with levels full of possible angles of attack (and full of loot and crafting materials). Your options for solving a given problem are also massively expanded with not just the improved environment few key abilities you have, but also with a ton of items, most of them craftable in-level so you can replenish your stocks of them (Lockpicks, death darts, sickness darts, acid traps, etc etc).
I haven't played a stealth game that good since Thief 3. No exaggeration.