Years 1-4 now has a demo on live arcade. I gave it a go, and it seems decent enough I suppose. 
 
My main issue with it is that it seems to make some real classic Lego game mistakes. First off is the sensation that every level lasts too long for its own good. This is probably my biggest problem with the series, that the levels drag on and on, even if you're not OCDing over collectables, which I often do after I finish all the levels. Second I sorta feel like the way it handles spells is crap, though I suppose they really couldn't have done anything but give us a stupid wheel of powers. Third I don't feel like the classes of character they have on display are varied enough, and the free play only gave me one more archetype to sample, that of the dark wizard. 
 
I feel that Batman sorta is the peak of this series. With its somewhat shorter levels, it managed to overcome mid level fatigue really well. Plus it managed an interesting mix of context based suit switching,  and traditional 2 character stuff with the villain chapters. From playing the demo, I don't feel that Harry Potter will top that. The spells should be more context sensitive, similar to Batman and Robin's suits, and perhaps a little more class based like the other games. I understand their intentions I suppose. They want to build a repertoire of spells to use in various puzzles, which the demo sorta shows with decent uses of Winguardium Leviosa and Lumos, having you stack blocks and Devil's Snare. But here's the thing, often times it seems its not really a puzzle, more of an excercize. There's no question of what spell to use when you run up to a Devil's Snare, it'll be Lumos. It'll always be Lumos. And I sorta feel the demo failed to establish if it'll always be that obvious. If whenever you see big stepping brings you'll get out Levitation. If whenever you see a mouse hole (I'm assuming here, I didn't see a mouse hole in the demo) you'll get out Scabbers. And while I suppose having each spell being that simple is fine, I don't see why it's couldn't just be context sensitive. 
 
I didn't really like demo honestly, and I doubt I'll get the game.

"My main issue with it is that it seems to make some real classic Lego game mistakes. First off is the sensation that every level lasts too long for its own good. This is probably my biggest problem with the series, that the levels drag on and on,"

I think I am going to skip it. I am completely over the LEGO games at this point.

The HP demo is my first go at a Lego game and I was really looking forward to it, but after about 45 mins yesterday I threw down my pad in frustration. I had no problems in the classroom scene, but after going to the Forbidden Forest I just got stuck... I used spells on everything I could find to move / blow up / etc, but all I was left with was three green tendrils and these square-shaped rocks that were emitting red sparks - but I couldn't do anything with them and there was no help I could find.
 
Sorry to interrupt this thread to ask, but what was I supposed to do at that point? I really want to like this game, I'm very much into the RPG/puzzle genre, but so far it's doing nothing to entice me.....

@Kaddion: Thank you - I'll try it again tonight and see how I get on.