After my conversion, I was introduced to Grudem's Systematic through a Evangelical (Semi-Pelagian?) coworker of mine (I hesitate to use the word Arminian, as his theology didn't seem to account for what Arminians believe, prevenient grace and all that). He had railed against Calvinism (I was too immature to know what Calvinism was right after conversion!) and he had Grudem's Systematic on his desk. Evidently, he never read it - as I pointed out shortly after showing him the chapters on Predestination, Conversion, etc.
So I will always have fond memories of Grudem's work. That said, I've drifted more into a Presbyterian/Covenant Theology framework - and he doesn't do a very good job on covering/explaining the Covenants. I also disagree with his eschatology, and I've drifted more into the infant baptism camp.
His ST is light, and highly readable. Newcomers to a Calvinistic background will find it easy reading and very understandable. I continue to recommend it to my friends. However, I picked up Horton's ST recently, and boy - do I feel at home with it. It's great, and fits my current perspective much better.
But Grudem's teaches the BIG TRUTHS in such a great way that the lay-person will find very understandable. Especially when it comes to controversial issues where modern evangelicals split from the Reformed tradition (Predestination, etc.).