Average pay; fast-paced consulting work leaves you at the mercy of the client; sometimes management won't stand up to client demands, leaving you with yet another 60-hour work week you won't be getting overtime for.
Great place to start for engineers fresh out of college; solid pay for older, more experienced engineers; difficult for middle-experience engineers (4-10 years) to do the grind. Hard to justify forgoing a more competitive salary at another firm for ten or fifteen years while grinding to become a principal and finally make serious money with company stock.
Mentoring is also ad hoc if you're not a geotechnical or materials engineer. Sometimes you're lucky and someone above you has the background and inclination to educate you on the finer points of being an engineer.
Terracon has a reputation as something of a meat-grinder with regards to personnel; it's getting better, but there is some of that mentality still.