I found the game was only really hard up to a point. Early on, my adept was having a lot of trouble keeping up with large groups of mercs, since the slow recharge time on my biotic powers (not to mention a smaller selection of them) relegated me to a playing the role of a really bad soldier, constantly pinned down behind cover. I quickly hit a turning point though (thanks to class investments and cooldown enhancing armour mods) where my powers seemed to be almost always available when I needed them, and the difficulty took a dive. Perpetual barrier didn't hurt either. The ridiculously strong weapons my companions were carrying around by then almost made even that a moot point though, since they were taking down most minor enemies before I had a chance to unleash my biotic storm anyway.
I'm hoping my current hardcore engineer run maintains the difficulty level even later in the game though. Not being able to stasis bosses and chip away at their health with no fear of recourse (bastion specialisation for the win!) should keep key battles a little more challenging, I think. Unless, of course, engineers become walking balls of death and destruction later in the game too.