It's fine for front facing seats. Rear facing seats are a challenge. I'm 6'0" and my wife is 5'6" and both of us are uncomfortable sitting in the passenger seat with a rear facing carseat installed. Currently we have arguably the smallest available convertible seat in there rear facing, the Combi Coccoro, and it barely allows some reasonable room in front. A graco snug ride makes the passenger seat unfeasible.
Bottom line, if you have an infant/small toddler and need a large rear facing car seat, the X1 is cramped at best. If you have an older child who can sit in a front facing seat, the car is fine.