The number of past shows varies based upon the age of the show, the network, and other factors. Some shows, Like Longmire in season 2 a viewer could only watch the previous week's episode, and that was it. Other shows, the entire catalog is there. With the more popular television shows, Hulu pretty regularly schedules "binge watching weeks" where many of the popular titles have the entire catalog available for viewing. ABC shows seem to have the longest run-time on Hulu on average. Some shows (like The Daily Show) have seriously lengthy back-viewing. Other shows , especially those from the NBC/Universal catalog tend to be on a shorter span. CBS does not provide new episodes at all, though back catalog stuff from them is on there and apparently Elementary will be coming to Hulu after season 4 begins.
The service is by no means a cure-all for cord-cutters. But, it does cover a ton of new content, and that will always be its niche - new content. For $8/month, viewers can get new content without the need for cable or satellite. They have the entire Criterion Collection available, as well as a number of other films. Films are all commercial free. Sometimes prime-time stuff is if the show has a particular sponsor. Commercials in general have increased over the past 3 years, a little bit each six months or so. They are still less than half of what viewers would get watching live. I would love a commercial-free model and be willing to pay a bit more for it, but the reality is that the sort of premium they would likely have to charge would put it back into a price range near to basic cable. So, I live with some commercials that I can largely ignore.
Hulu shines the most during the regular U.S. viewing season, when most shows are next-day viewing. During the off-season, it still has plenty of use though, as that's when it works nicely for catching up on or getting exposure to plenty of foreign shows that have no U.S. market. I've found plenty of shows I enjoyed that way. They also do original programming like the other two services, though none are anywhere near as popular as some of the ones on Netflix.
Overall, Hulu+ probably rates a C+, or maybe even a solid B. If they ever add in new content from CBS, or if they ever do embrace an ad-free solution, they would become an almost essential part of the streaming age. As it is, they leave a few things to be desired. Still, I can't knock it for the cost.