First let me start by getting a quick comment in that someone is sure to post. Airguns are real guns. You will be surprised at what they are capable of.
Next it would be good to know what you intend to use it for. Targets, hunting, plinking, what ranges and so on. As with anything the quality you get will be directly related to what you are willing and able to spend. You mention pneumatic and I am assuming you are probably referring to PCP's (pre charged pneumatic). They aren't my area of knowledge but you can certainly find whatever level of quality and capability you are looking for.
At any rate quality is definitely available. It can equal any powder burner you have.