I've played an arcane trickster to level 20 and it has been one of my favorite characters. yeah your weaker on spells. But SKILLS SKILLS SKILLS it got to the point where my gm was like "I don't need to roll for your elf secret door search anymore your search is so high you get them automaticly."
Low levels is tough... I took PBS and precise shot. Had a decent dex to make it effective when your out of spells.
Mid levels are decent... an improved invis and your bow goes a long ways in a battle
High levels rock. you look over at the big nasty thing... raise and eyebrow and mention... "I'm going to sneak attack you now. then drop a polar ray on him with an extra 8d6 worth of damange no save... MOHAHAHAHHAHAH