Yoh is quite dull (not in the dense sense but in the boring sense).
Haruna is quite the opposite, a bit dense and naive but cheerful and all, and all the other chars are honestly just side characters you can toss away (Fumi the ever-smiling dork).
Nonetheless it quite entertained me even when I temporarily dropped it in the middle of vol 6, last year, because it can turn so ridiculous that I was fed up with it. I recently picked up and caught me getting captivated by it again.
The stories are all known, nothing new, very very light (don't expect more than holding hands and about 8-9 kisses in the entire series), often very cute but not very deep (well I said that already).
The chars don't change that much either (Yoh at the end is still dull) but it had its funny moments I could really laugh my arse off, thanks to Haruna.
The end is light and boring too, (ok, Haruna's appearance was once again a big LOL) ah well... it's good stuff for young teenagers and something to pass time for all others.
I give it a 7.6 for its humor, for Haruna's cheerful and weird character (quote from Yoh 'I think I got myself a boyfriend instead of a girlfriend' XD) and Yoh's art that was often very pretty (...oh and Akito too ^~).
If you like such kinds of stories I suggest Hana Kimi, it has better characters (and even the side chars are memorable), more humor, longer story with more development but also nothing very deep.