Always make it a point to go to at least one concert here in the summer. Its very lively and even with Lawn seats you can see the whole stage! Only downside is that the back half seats are not covered so not so great if it rains. That being said I have attended concerts in the rain here and its still great regardless.
Only downside is actually returning from the concert if you live in the GTA, Go train has more regular hours now so its a bit easier since Its right next to exhibition go station. However, last time I was there i had to take ttc and the streetcars were not that regular late at night.
Note: Parking is a flat charge of $20