Not too bad - as long as you have a pretty comprehensive reference manual to work off of, good set of tools, and a second vehicle to get those parts you may have missed and need to get.
I will assume this similar to a V6 Camry - will need to remove an engine mount and secure the engine well. Not very hard to accidentally knock the timing out of whack - so you need to keep the (gears) cams from turning on you. Might as well repalce all the v-belts and change the waterpump while your in there - be a pain to do all that only to have the pump fail soon afterwards.