For as obvious as the first few puzzles were (the pause after you solve a problem seems just a tiny bit longer than it should and makes the first handful of levels a bit annoying,) the level design here ended up being a very pleasant surprise. Right around level 18 I started having fun, and when levels started having 3+ light sources I actually had to start thinking.
There's a lot of fairly obvious puzzle elements here, with the typical systems of solving them; mutual exclusion, backtracking, etc. but a few of them (typically ones that involved multiple light sources sharing a mirror) were really clever. I also really liked that the light beams were nice and generous, making it so that it almost never felt like you were finessing a pixel-perfect solution even after figuring out what you were supposed to do (Nodes had this issue and it could be a real pain.) The beam-splitting levels at the end drifted into this territory a little bit.
It was a bit annoying to have to go back to easy levels once you started exploring the "one source hits multiple targets" mechanics. In fact, it might have been good if you'd formally divided these levels into sets (1 source 1 target, 2 sources 2 targets, 1 source 2 targets, split the beam, etc.) so that the ordering of the levels actually made sense.
A lot of the puzzles that had an obvious partial solution also ended up being annoyingly easy. It's pretty common for puzzle games to throw in "bait" to make players try wrong solutions, but your bait is too obvious.
The later levels (40ish) can end up being a bit overwhelming due to the raw search space of the problem, though the all-45-degree mirror puzzles struck me as more tedious than anything. It felt like I was solving a maze, which was a pretty sharp contrast compared to the earlier ones. Toward the very end (50-55) the puzzles got so complex that I really didn't understand what I did even after I solved them. Being able to pause and look over my own work would have been kind of nice (especially since I finished several while still having mirrors left over.)
It does strike me as a bit odd is that the mirrors are stuck in their orientation. For the sake of the puzzles it makes sense, but I wish there was some in-game explanation for why you're not allowed to rotate them yourself.
I also wasn't a fan of how the same graphical elements are reused for every level. It wouldn't be asking for much to add just a little bit of variety. Similarly, the targets you hit look kind of lame. Plus, Unity affords you so many cool tools when it comes to shaders and textures, why didn't you just use some easy presets to make something look a bit fancier?
Some definite design flaws but overall a really good game. I usually don't stick with puzzle games long enough to finish them but this one was worth it.