Mx0, in my opinion, is probably the best comedy series I've read, and is definitely in the running for best romance and best action. The setup of the main character accidently becoming part of a world he doesn't understand might seem a little contrived, but was executed so well that it came across as completely unique.
Another thing that is unique about it is that even though it's ecchi, it isn't a full on harem, as the MC, Taiga, quite clearly maintains affection for the heroine. Another refreshing break from standard ecchi plot comes with the fact that the MC is so honest and dedicated that even when he's placed in ecchi situations, the girls think to give him the benefit of the doubt.
Furthermore, the MC, who can't use magic, counters all of the other magic users with little more than his wits, super tough body, lies, schemes, bluffs, tricks, and a determination that would make shonen protagonists proud. Not only does Mx0 give us an awesome protagonist, but it also has tons of minor characters, each with their own personality quirks. However, despite all the characters in the story, each one seems to be used to their best potential, and I never got the feeling that "oh, they could have expanded on this character a little more".
Considering the plot revolves around the MC trying to prevent getting found out that he's a muggle, the fight scenes are excellent, with Taiga loading on the BS of being a "master wizard" scene after scene. The author knows exactly what points of a fight to play for drama and which points to play for humor, and the jokes are clever and hilarious. The only thing I thought could be improved was that the story was somewhat lacking with only a few major arcs and no real villain; but that was because the story was so good I was fooled into thinking it was an action series, instead of a comedy that doesn't need a villain to be engaging and enjoyable.
All in all, Mx0 was an engaging, fun ride all the way through, and when I was done I wanted to read it again. The biggest problem was that the series was abruptly cancelled just as it was getting good, leaving me wanting to see more of these characters I'd grown attached to. The ending felt rushed and disappointing, and I can't help but regret all the potential lost. If you're looking for a good, quick read, and a laugh or twenty, you can't go wrong with Mx0.