I loved the Dragondawn's Adventure to the Enchanted Floating Islands. Hopefully we get some more things like that.

With regards to your questions

500 characters seems good to me.

I feel like with reviews regardless of the item (Polls, madlibs, word searches, poems, writing, essays) the effort to writing a review out and sharing feedback to authors is more or less the same especially if there is a character count required. I don't think there's an advantage in limiting reviewing to particular item types. It would just mean there would be less items available to review overall.

I've been doing a lot of video game product reviews myself since I was a fun opportunity to write about my opinions on various games I played. On my end while I love having the option to be able to review games I'll be ok and adapt if you prefer to make product reviews book only.

My recommendation though if you do decide to change or modify any tasks or point values maybe provide a couple of days notice to give us a chance to adapt to them if they wind up making things more challenging for us. I plan a lot of my writing / reviewing strategy in advance so it would be helpful to be able to adjust accordingly.