1/Overall writing - excessive scripting, some truly awful stories full of gaping plot holes and terrible dialogue, bland uninteresting characters, lack of dialogue options for the player or decisions with consequences. My major gripe. I firmly believe Bethesda badly needs to sack whoever comes up with this drivel and hire some writers.
2/Maybe should be part of 1/, but game design that constantly tries to railroad the player and assumes they automatically want to be a combination mage/warrior/thief. In other words, aiming directly at the lowest common denominator mass market player.
3/Race doesn't mean anything - there's a whole really interesting potential mechanic that is being ignored. Presumably to avoid upsetting the legendary 'casual gamer' in some fashion.
4/Inexplicable absence of any kind of optional hardcoe/realism mode. Mods are there but can be very buggy. And game isn't designed with it in mind which doesn't help.
5/Can't walk past NPCs without them constantly repeating the same inane lines over and over again. This is probably the leading cause of homicide in Skyrim. The Skyrim my characters are in that is.