Starter, alternator, EGR, O2 sensor, timing belt, and fuel pump have been the major issues for our Rodeo.
I wouldn't recommend getting one as a daily now though because getting parts for it is starting to be a bit of a PITA and when Isuzu pulled back/scaled back in the US it's made it even harder to get answers. When we ordered the O2 sensor, we wound up getting five different ones all using the same part number until we finally got the right one. Each box had the same part number and UPC, but each sensor was different.
We have the 3.2L and it's presented some really odd trials...the alternator is essentially underneath the car and to replace it you need to spend a good 3 to 4 hours of labor to include taking a damn wheel off. To replace the starter you'll need to take off a header or you're going to do allot of cursing and screaming.