That depends, are we talking good as in critically, or profit? Illumination has done a very nice job of making a profit out of realatively "cheap" films. (Granted $60-70 million ain't cheap, but it is when you compare it to Pixar and Dreamworks who are giving their films budgets of $130-200 million.)
Though admittedly when it comes to the films critically, it's kinda hit or miss.
Despicable Me - In my opinion so far it's the best film they've done.
Hop - It's a mixed bag, kinda middle of the road.
The Lorax - Ho boy...for me this is right up there with the live action Cat in the Hat as the worst Suess film adaptation. (It's also why I'm incredibly nervous about their upcoming The Grinch film.)
DM 2 - It's a nice film, but not as good as the first.
Minions - It's alright, though compared to the DM films it's on the weak side.
Without a doubt Illuminations will be making films that'll make quite a profit, question is will they be able to make films that'll be right up there with Disney/Pixar and Dreamworks best which are very highly acclaimed? Looking at the current lineup for Illumination...
SLoP - It'll do fine finacially, but with it being a pet version of Toy Story and some voice actor choices ain't winning me over.
SING - No. No. NO. Go away jukebox musical that's oh so proud of all the friggin' songs it's using, go away.
DM 3 - It's a wait and see, but we know how the third film hasn't been good for most series.
The Grinch - As I've said before, thanks to how they did the Lorax I'm quite nerveous about this.
...Right now I'm gonna' say not yet. I really hope so down the line, but I don't see it happening in this group.
I may be really critical about that, but that's because I want to see this studio do really great films. It's good they're making a profit with their films, but I don't wanna' see it turn into another Blue Sky where they're churning out terrible/lazy sequels after another because those are what make the most money. (Like Blue Sky is doing with Ice Age.)