It is a good phone. That being said, it is getting to be a little dated (2 years is a LONG time in tech!)
So if you have a 4s will it continue to work, work well and reliably? Sure, provided you dont break it. But will it be as efficient and powerful as a 5s? no chance.
You use "good". If you want a better answer perhaps explain what youre looking for exactly? My father's BlackBerry bold 9900 is also a "good" phone. I have a buddy who is a dinosaur and has a samsung flip phone, which is also "good". All he ever uses it for is as a landline replacement, functionally its great for him!
Anyways, decide whats important in a phone for you, because "good", may not be good enough. For me, the 4s wouldn't be "good enough" to keep me satisfied in late 2013.