How relevant is the iPhone 4?

So now that my old Android phone is at the end of its life and I'm moving on to finding a new phone to replace it, I've stumbled across the iPhone 4. Now, I'm a pretty budget-conscious student, and I like to avoid phones that require a certain tier of monthly payment (ie: iPhone 4s, 5). So that's why I'm thinking about the iPhone 4, and not the 4s or 5.

Now what I am left wondering is whether or not getting the iPhone 4 would be a good idea. Does anyone still use the iPhone 4 without complaints? I know there's a pretty big specification gap between the 4 and the 4s, but could the former still be a good phone?

Update: Thank you everyone for your replies. I have now realized that while the iPhone 4 is still a relevant device, and also while some people still enjoy their devices as old as the 3GS today, the iPhone 4 is becoming outdated. I have decided to take the advice of some users and go for the iPhone 4S, which I was able to find at a reasonable price on a decent contract. Thank you again to everyone who gave their opinion!