This is going to depend on a number of factors.

The newer 738s with the Boeing Signature Interior are pleasant, but the new slimline seats are among the least comfortable I've ever sat in, and I'm not even that tall. There is power between the seats, but my chargers always fall out really easily.

Always make sure to download the United app so you can access the Wi-Fi entertainment, but that's not guaranteed. Whether or not you'll get a seat back screen is unknown. IIRC, there are non 738s without entertainment, but many only have the drop down video screens which are totally worthless IMO. Chances are your 738 will have seat back DirecTV.

Without knowing what route you have (and even then), it's really hard to say what the experience will be like. United has a lot of 737s (many of them -800s) and there's a lot of variability in the fleet.