Although I have to agree that the game suffers terribly in places (NPC dialogue, some combat aspects, next to useless map), I persevered with it and am now thoroughly enjoying it as a semi-serious alternative to Oblivion (which I have clocked up over 100 hours playing).
It may not be as immersive as Oblivion, partly due to the lack of a true first person persepctive (it switched to 3rd person as soon as you draw your weapon), and the graphics are not as polished as Oblivions, but it does have something to offer (not least the lack of long load times when moving between towns and countryside etc, as result of Oblivion's good looks)
Quests are just as much fun as Oblivion, and although the map does not really help you to work out where the hell you are going, this is in some ways better than Oblivion, which I found was a bit to 'guided' - you always knew where to go to complete each quest, so it took away the exploring aspect. This harkens back to the days of 'Morrowind', and I found it quite challenging to go wandering off course, hoping I'd make it to the right place - more realistic in some ways than Oblivion.
Upgrading weapons is another feature I really enjoy, rather than relying on adding spells to a weapon and then worrying about using it and depleting them, you can combine multiple copies of the same weapon together to make it more powerful, and can imbue it with one or more elemental properties (well, fire, ice, electricity, spirit & poison). These powers don't then dry up in the middle of battle, leaving you with a pretty weak sword (eg Umbra).
I could go rambling on for quite a while about how I'm enjoying killing every Orc i can find and selling their possessions so I can upgrade my armour and weaponry to the max, how it is really rewarding to kill a dragon or Golem that has been kicking your sorry ass every time you've previously encountered it, having upgraded your swords and pinched some better armour off of a bad guy you've just wasted etc, but I will leave it up to you to make your own decisions.
I wouldn't recommend this as a rental game, as you need to spend some time getting into the game and playing the side quests and exploring all over the place. While it is true that it doesn't quite live up to Oblivions extremely high standard, it is a decent game in its own right, and doesn't deserve the mauling that some of the reviewers have been dishing out, presumably based on a few hours of gameplay. I was willing to join their numbers until I gave it the benfit of the doubt for a few more hours, now I'm choosing that to play over Gears, Pro Evo, Stranglehold, Stuntman etc. It is my game of choice at the minute, and I can see it remainng so until Halo 3 comes out (that'll be next week then!)