Pros
If you're lucky enough to awarded a Graduate Teaching Assitantship in the English department, be prepared for an intense two years. As a teacher, you'll be closely guided by experts in the field and may be able to not only teach composition but poetry, fiction, non-fiction, or TESOL. Best two years of my life and I miss it!
Cons
The pay isn't great but the tuition waiver makes it worth it. I don't have first hand experience, but have heard it can be difficult to advance in any department and the salary is considerably lower than other state universities. Springfield is a fine college town, but may not be somewhere you'd want to settle. The Queen City of the Ozarks is also in the Bible belt; something to consider if you're not a conservative Christian.