I watched the first 3 seasons of ZnT after hearing the OP of the 1st season and wondering what anime series it came from... weird reason to watch an anime I know but it is what it is.
I really enjoyed the 1st season - the storyline, the fantasy world, travel between two worlds - it was all so interesting and unique. The 2nd and 3rd seasons were good but not as good. It felt like the fanservice got in the way of the story at times. I was glad to see this final season returned to more of a winning formula by focusing more on story and the characters relationships than fanservice. Don't get me wrong, it's still in there, but not as over-the-top as it felt during the middle seasons.
Technically the animation is very good, clean and bright for the most part. I enjoyed the OP and ED from all the seasons but the 1st OP was my favourite. BGM was well done and helped set the tone for the on-screen action.
The strength of ZnT lies in its characters and the skill with which the VA's bring them to life. I've really enjoyed listening to the dialog in this series and I have to give credit to the VA's for the excellent work they've done!
Thankfully, they chose to end ZnT on a high-note and really the only way you'd expect it to end. I have to admit that ending made up for a lot of the disappointment I felt from some of the overt fanservice and the occasional 'fluff' episodes that are present in almost all short romcom anime series.
Zero no Tsukaima has been a very enjoyable anime experience for me and despite some of its shortcomings it pulls through with a great romantic ending.