I'm not too inclined to write reviews of unfinished series, but so far (ep4) to aru is looking promising enough.
It isn't necessarily an outright 5-star anime, imho; while the story is ambitious, it is also slightly disappointingly executed in parts (notably the often astonishing fight-hax Touma seems to get, i'm still a little grouchy over the Touma/Accelerator farce).
Similarly, while the dialogue is often pretty excellent, with supporting characters and enemies capable of creating real interest ...spiky-kun seems to get some awfully cliched lines at times.
The animation is good quality, up-to-date. It probably won't wow anybody who hasn't arrived here via a time machine. The OPs are good, though.
What makes this a 5 star anime, in my opinion, is the fact that it's fun to watch. It's well paced, has a fantastic cast of characters and it plays with some interesting concepts.
I am also going to have to admit that i think any series where the protagonists unabashedly beat the cr*p out of an army of psycho nuns is, you know, pretty great?
Still, for me the real entertainment will be later in the season; we've yet to see many of the best characters get screen time (accelerator + the sisters network woot) and going from the light novel plots I suspect the anime has a lot more in store for us.
