Grimgor- always an excellent choice
Orc Great Shaman- cannot have magic armour, other then that decent.
NG shaman- good option, I like having NG shamans in a list to deaw out dispel dice while overpowering spells with their mushrooms.
BO BSB- excellent option.
NG big boss- not bad, but it seems lacking not to give him a little magic gear, even if its something cheap and easy like enchanted shield, warrior bane and the devastating charge potion (always forget the name). Personally I would give him warrior bane, and the potion of strength so you can use his high initiative to smack a nasty enemy at S7 and mebbe knock them down a peg or two (and gives you more anti-etheral).
Da Immortalz- excellent unit, mebbe needs a few more orcs in case they get battered by artillery (nothing much will compete in combat).
Big Unz- don't think they can take magical items. I like the unit set up and numbers.
Goblins- like the unit, other people might not like it, but I think goblins and skulkers are funky. I would give them a musician for sure (for fast reform to shoot elusive enemies and to help rally) and possibly a standard if you play the book missions (for blood and glory).
Spiders- I don't think you need 3 fast cav units of 5 models...
Night Goblins- good unit. Depending on how you use them I might add an orc hero with GW to give some S7 attacks and so they can't panic from other goblins (chances are if they got beaten in combat the orc would die anyway so is less likely to cause orc unit panic checks).
Giant- bit rubbish, I just wouldn't bother taking a giant anymore. Either cut him completely for more infantry or try to find the points to upgrade him to an aracknarok: the extra wounds, toughness, armour and attacks make it a much better investment (plus its a pretty immense model and a nice centrepiece).
Rock Lobber- probably not as good as a doom diver, but depends on how much you rely on it. I've just bought one and hope to play test it a little.
Wolves- as I said I don't think you need 3 fast cav units, but they are fast, cheap and with S4 should do you quite well against weak flanking units.
I think you need a little more random in your list: not just to make the list better as such but just to make it feel a little more orcy
I suggest either some mangler squigs, pump wagons or mebbe just some more fanatics just to make your lists a little less predictable. Personally I'm a huge fan of pump wagons and doom divers, both are immense. I also like small savage orc units run as flankers: given AHW and run up a flank they'll massacre anything they meet and will cost <100pts, they would also help turn hard fights that your bigger infantry units might get locked into.