I have been a long time 870 user, specifically a 14 inch model, for my Alaska walk-abouts. This winter, I decided to try to find a semi-auto shotgun that might work for my criteria -- reliable, reasonably accurate, lightweight, fast shooting, comfortable to carry, reasonable length of pull, stock suitable for aperture sights and a H1, and able to shoot a range of loads.
I stumbled upon the newish Beretta TX Storm shotgun, got one, and so far have been very impressed. It feeds everything from low brass bird shot to Brenneke slugs, cycles fast, weighs only 6.4 pounds, has an appropriate length of pull, and a terrific stock that is comfortable in recoil and set up with a proper comb height for aperture sights and a T1/H1. You can even co-witness the aperture sights thru the H1. Most excited I have been about a semi-auto shotgun ever.