Portal 2 is very polished and has nice dialogue and some nice puzzles, but it’s just much more restrictive.
For me the issue wasn’t so much the gels as the ‘moon dust’ surfaces. In Portal 1 the portal gun basically worked almost everywhere, but in Portal 2 there was often just one white panel that just happened to be in the right place to launch you towards that other white panel, etc…
Valve are great at drawing attention, so there’s usually be a light or something to draw your attention towards the correct spot for your portal, and then something else for the next one. The net effect was that it felt like there was one proscriptive and somewhat artificial solution to each puzzle, and you were kind of led by the nose through it.
I mean, that’s fine, and it probably allows them to craft more complex bespoke puzzles, but it’s not really how I felt about Portal 1. It’s closer to Monument Valley (which I also love) and a lot of the portal-likes that followed.
Portal 1 clearly had an intended solution for each area, but you could effectively put portals anywhere, which meant that you could experiment a lot more and come up with alternative solutions (something I doubt you could do at all in Portal 2). And even when you did come up with the intended solution, I felt more like I’d come up with it myself rather than been lead to it.
Playing Portal 1 a second time, I could come up with solutions to shortcut huge parts of the puzzles. The same thing was rarely possible with Portal 2 as it was just too ‘polished’.
(All of this applies only to the single player. I hear the co-op has more of a Portal 1 vibe, but haven’t had a chance to try it yet).