At first, I couldn't see why the developers didn't just use this mechanic straight away. But then I saw something brilliant, the game "broke", and the game mechanic was unleashed (as if by accident). As the game started to glitch and go crazy, I was half like, nice I like those effects where the text characters appear in weird colours... but then after a while, because the effects looked so realistic, I was sort of half-worried, in the back of my mind. Is it really freaking out, what's going on? Then the BIOS screen, oh, ha-ha, nice. They even included a sound effect of the hard drive spinning up... that took me right back. Then the game restarted... oh crap. Nah, it can't be broken. Ah, there's a Fez on his head so at least that much is saved! Oh, what's this, different perspectives? Awesome.
I read on Wikipedia that the 2D/3D game mechanic is to Super Paper Mario and Crush, to quote:
Fez features 2D/3D perspective shifts in a manner similar to Super Paper Mario and Crush. The use of Escher-like optical illusions also predominates gameplay in a manner similar to Echochrome.
Not being able to die in the game allows the player to focus on puzzles, and worry less about technique (at least in the beginning). Later, in level 3, instead of falling to your death you fall into the water, so now you start to focus on your technique a little more. Actually this was my first "noooo!" moment, and the timing felt right; I've invested enough time in the game so far that I'm happy to try a few more times to overcome this damn tower level! Eventually I cracked it before my patience ran out, so now I'm even more invested in the game. Technique gradually becomes more important in later levels, where you use the classic mechanics like: Taking a run-up will make you jump further.
The game gives players hints to the locations of cubes, and the world map shows which levels are yet to discover and whether or not you've got all the secrets. This gives you plenty of value for money, in that you can really get the full experience from the game. I can imagine that some players might not like the secrets being advertised like this, but I think it makes the game more accessible.
Interesting, that in the 2nd level, it's much easier to find cubes than in the 1st level. This could be to get the player used to the slightly higher degree of skill needed for jumping between platforms. It's still hard, but in more of a technique way, than a treasure hunt way.
The "dot" is quite a funny character, going from comments like "it's like some important... door... place..." when describing a place with lots of doors. Just my kind of humour.
The developers have really used the perspective mechanic to the game's advantage. You have to rotate the view to a specific angle on some levels, to find the right path. Often you need to switch back and forth between views to progress -- these puzzles must have been quite tricky to design.
Features like the inventory are introduced gradually, which is a nice way of building the tutorial into the game. Also, the "dot" character is aware that players don't particularly like long, wordy dialog; at one point it even says "OK, now I'm done, I swear!" in reference to the amount of dialog used.
There are a lot of game elements that look to be inspired by Zelda; the style, sound effects, assistant character, the atmosphere, for example.
Puzzles get even more bizarre and mind boggling as the game progresses. Such as the ability to climb directly up 2 totally separate ladders as if they were one. From the side-on perspective, climbing seamlessly up the ladder is not possible...
...but rotate the view 90 degrees, and you're able to climb up as if it was one ladder...
This is actually one of the more subtle uses of this mechanic. In fact, as the game progresses, usage of this strange mechanic increases. Soon you're able to jump between platforms that in a 3D world would be totally inaccessible to one another. The game's idea seems to be that each perspective is actually a slightly different world, yet they all join up seamlessly (much like Echochrome). At one point before you are introduced to the 3D mechanic, one character says "Reality is a perspective, and perspective is subjective." which I believe is a brilliantly subtle reference to this mechanic. Solving puzzles using these different perspectives can make the player feel quite smart. I felt pretty smart when I had rotated two platforms to match each other form a particular perspective, so that I could cross them (even though in hindsight this seems very simple now). I thought to myself "yeah, I actually get this now."