The Mossy 500 and the 590 are damn fine guns, so... if the 88 is a step down, it may still be worthwhile gun. You'll have to determine that. There are plenty of web reviews
that say the 88 is solidly in the "Good Enough" category.
If you're looking for used... don't ignore the Mossbergs. I've got a 590 20" Special Purpose/ Persuader. It's been used and abused, and never bobbled. It also has IMNSHO superior ergonomics to the 870s (and Maverick 88s.) Chiefly, the Mossbergs have a tang mounted safety, much better than the cross bolt safety ahead of the trigger guard.