I played both last year for the first year, back to back.
I really liked SS a lot, but First Light, from a pure gameplay perspective, really hit the right spot for me, the slow motion weakspot shooting was extremely fun and getting a crazy combo going in that "training" part of the game was really satisfying. Good sound design and visual feedback and some of the later missions were insanely tough with 10s of waves but I don't know why losing the combo never really frustrated me because the gameplay was so fun the completion of the challenges was just a bonus, the skill points gave a good feedback loop for unlocking cool new stuff like the burst nearby enemies on death skill
The neon movement in First Light was improved in a few small ways but just that made it a lot more fun than in SS, that needs to be the template for a Flash game's movement if one is ever made. When I had access to the City and picked up the first collectible I just didn't stop until I had them all, maybe 30-45 mins, it was so so satisfying.
The character face tech is really impressive in the game, a few standout cutscenes I still think look better than almost everything else since, the story is a bit mad and felt all over the place in terms of pacing but I was doing the side stuff in between so that probably made it worse, still had fun with them most of the time though. The story missions were actually pretty good for the most part with good variety in what you were doing.
The side missions and activities were mostly fun but the security camera one was a bit rote, felt like the CPU was cheating you with how fast it moved but its like pigeons in Spiderman, even if kept up with them for the first 5 seconds or so you would be blocked from capturing it until a certain point, I know its just in there to stop it from being trivalised but it felt like you weren't being rewarded for having quick reactions.
I don't mind silly spray can motion stuff, at least its different and there aren't so many to make it annoying. The graphics in general are pretty spectacular still and the HDR presentation is one of the best I've seen, you really need to set the contrast to "low" to make it look right on a VA FALD LCD or OLED, otherwise the blacks are nearly crushed. It might be more tolerable if you have gamma at 2.2 (usually default gamma or "low") but its still mental, they added the contrast low setting after they realised they had tested the game on lower contrast displays and not realised this would be an issue with the previously mentioned panel types.