Is this a good bike??

Just my opinion, but it looks to be pretty poorly maintained, lots of wear showing outside storage, like rust on the chain and work tires as well as a weathered seat. Nicer bikes and really BMX bikes in general aren’t super high maintenance. But when you start looking into the somewhat lower end you’ll start to run into issues, I would say ask if the bearings are sealed, ask about maintenance done to it and ask about more specs and stuff. Without knowing brand and model it can be hard to advise someone. But, if it has unsealed bearings I’d stay away, given that it looks like it’s been in a good amount of water, you’d like have to replace all of the bearings and chain as well as some bolts, if your looking for a pretty build probably all of them.