Having just finished Dead Space 2, I definitely prefer the first game, though I still liked the sequel and had a good time with it. The second game has more more fun combat and arguably more mechanical depth, but I found the level and encounter design frequently lackluster and the pacing was really off for me. There were a few moments where I could see great potential in the game's shift of focus, but overall I think the first game was just more cohesively designed. I'll go point by point:
Weapons are better than ever, with more options and better balance, plus the resource distribution seemed a little more fair. In DS1 my loadout was Plasma Cutter/Line Gun/Pulse Rifle/Contact Beam, while in this game I opted for Plasma Cutter/Javelin Launcher/Pulse Rifle/Ripper. The tweaks to the weapon upgrades were all good too. The stomp is amazing, and impaling enemies is awesome. At first I thought stomping enemies for loot was just busywork (fun busywork), but I realized that it actually makes encounters more dynamic since bodies disappear and you want to rush to stomp or try to overkill to get more resources. The new armor system is disappointing (linear upgrades to protection and inventory capacity were an interesting choice because you could skip tiers to offset their expensive cost, vs DS2's meaningless "choice" between obviously superior armor perks), but inventory management is a bit tighter, and the dynamic loot system no longer heavily incentivizes Plasma Cutter-only to the same degree. I also like many of the new enemies, particularly the Stalkers, who always made for excellent fights.
Where the game disappointed was in the level and encounter design. Most of the early game was corridor fights with a single enemy type as the roster was being introduced. This was acceptable, and the game started to mix and match enemies at a decent pace towards the midgame. By the time I revisited the Ishimura, I felt the game was finally coming into its own, and hoping for more clever encounters. Towards the final third, though, encounters started to veer downward as I found myself fighting waves of the same Enhanced Slashers and Pukers in every room, where I'd be lucky to find a single Exploder to mix things up. The enemy roster itself is fantastic, but they're so underutilized. I remember the first game never running out of steam on this front, with new combinations of enemies in environments that would test my ability to form moment-to-moment strategies and sizing up every new room I found myself in. Infectors made me scared of any room with corpses, I had to leave Pregnants a wide berth (heh), and Lurkers had me checking high walls and ceilings. DS2 has more focus on twitch reactions which is a load of fun, but gets stale when I'm fighting the same predictable enemies over and over.
I also prefer the first game's structure. It was still linear, but you often had more freedom to explore decks at your own pace with a lot of variety in the challenges and puzzles on offer. Hydroponics was a highlight for me, and I loved how the game was able to reroute you through the decks and set up new challenges in familiar areas. Puzzles generally required more critical thinking and was more integrated with combat in the first game. I was particularly disappointed by the spacewalks. Is it more fun to fly around like Iron Man in Zero-G than to jump to walls with clunky magnet boots? Absolutely, but the game doesn't do much with it. The first game had more Zero-G and vacuum areas overall, not always tied together, and they were more distinct and challenging. I have great memories of tense spacewalks with moving obstacles and ambushes from silent Necromorphs all on a strict oxygen limit. The vacuum sections in DS2 are a complete joke by comparison, and I pity the fool who spends a single node on upgrading their air capacity. There were some Zero-G segments I really liked, but the lack of meaningful puzzles and combat for many of them was a disappointment overall considering the freedom of movement.
There were still some great moments, at least. While I was immensely disappointed with the lack of payoff in the Regenerator sequence at the end (the first game had two brilliant "you're terminated, FUCKER" moments), there were times when the game did some cool things to surpass its predecessor. A highlight for me was when the game showed me how airlocks worked, and then a while later put an Exploder next to an airlock and required me to quickly shoot the button to close the emergency shutter when I instinctively blew it up on the spot. The Stalker fights were all sublime as I said before, particularly the one with all of the Cysts and shipping containers. The whole Ishimura revisit was particularly superb. The slow build of tension as I crept through familiar hallways haunted by the past until an explosive fight suddenly broke out on the bridge was probably my favorite moment with the whole game. The Church of Unitology was also fantastic, and I liked some of the action setpieces, such as getting ambushed in the space elevator or drilling through to the Government Sector. These fresh moments were when the game was at its best, and I was most impressed by the new direction. If some of the content in between had a bit more variety and better pacing, I think I might like it better than the first game. But overall, I remember my time with the first game more fondly.