I didn't realize that you could go underwater and explore. I went though a couple places that I could have done that if I had know.
Yep here's a couple of pic's
http://steamcommunity.com/profiles/76561198052828093/screenshot/488877970003942847
http://steamcommunity.com/profiles/76561198052828093/screenshot/488877970003964810
Those look like they were taken in Ilinalta's Deep.
I wish I knew that mage armor and ebony flesh svcked and I wish I had known that robes in this game were going to be lackluster. Had I known I would have invested more in smithing. Also I wouldn't have taken the bonus perks for damage in Ice and Fire. I should have just stuck with lighting.
Oh and had I known how weak conjured weapons were compared to smithed ones I wouldn't have taken that first perk to buff their damage in the conjuration tree.
The Bound weapons
are pretty poor next to smithed stuff, but in trade you can get them pretty much right off the bat while the good crafts take a while to come by. I still use them, though, because my Conjurers don't carry physical weapons. Then again, said weapons aren't their main means of combat anyway, so don't need to be smithed to insane levels.
If there's one thing I wish I had known ahead of time, it would probably be that fully investing in most perk trees is a complete waste. Ended up restarting my first character four times due to wasted perks (I'm fussy that way) thanks to that.