|A few others that have been made, but I'm only focusing on Mewtwo and Eevee, as they're the ones I actually own|
Well, starting off with the looks, they do their job well. If you get the angle right, they are basically sets of the Heart Gold/ Soul Silver overworld sprites, and at this size, they do look very cute. As I said though, these basically just sit there, they don't do much else. Granted, they don't need to.
However, I do need to stop the praise there. While I cannot speak about the rest of the sets Nanoblocks has put out, I get the feeling some of what I'm about to say applies to more then just Mewtwo and Eevee. For one, the design for some parts seem to focus more on the look rather then the tolerances of the pieces. This mostly applies to Mewtwo, due to his ears, arms, and cord on the back of his head (while building) are a nightmare. There is not enough friction in these locking points at times, and made worse when you're putting weight on a (to use a lego term) one stud lock. I actually had to modify Mewtwo to better secure his arms, and to add better feet. Mewtwo, thanks to its tail, is very back heavy, and with no heal spurs of any kind means its going to topple over a lot. Eevee is also easy to knock due to piece position, but that's limited to side to side. The instructions on these were also, while not the worst I've seen, could have been better, as they feel like they were running out of budget and had to limit the instructions to a page. Add to this the tiny pieces which a 1x1 piece is barely bigger then a small birthmark on the palm of my hand, and I can see people getting frustrated very quickly. Finally, while I am still tossing up whether to call it a benefit, or an issue, there were a lot of spare parts for both of them, and combined with them being hallow for the heads (no I'm not making an airhead joke), and you get the feeling you've skipped steps, but that might be my Lego experience talking.
If all you want is to have these, or other sets being on your desk at work, or to put on your book case, then these will fit that role well. On looks, they do their job well. Its getting to the completed build, and keeping it complete, that issues start showing up. I dread to think of things like the Eifel Tower as Nano blocks if build issues like with Mewtwo are common. Come Wednesday, Ghostbusters II, and next Sunday: