I really love the IRIS Top Entry Cat Litter Box. And so do my cats.  I was a little worried about it being top entry and if they would use it but they do and it is amazing.  No more cat litter everywhere.  I no longer have to sweep near the litter box daily which is so nice.  Only draw back is it is for adult cat I dont see kittens being able to use but for my house that is perfect.  It has a large opening at the top for the cats to enter and exit the litter box and so far they have been able to knock it over like they did with their old box.