That is quite an uneasy question to answer given that WhatsApp supports multiple platforms, but I will try and sum up as best as I can.
I myself use this app on the Windows Phone and Android platforms so that's what I will cover.
Is it becoming better? One would say yes to a greater extent but it depends on how you are looking at it. The constant updates are mainly due to issues such as bug fixes and improvements, which makes the download a waste of (precious) data especially if your mobile is not affected by those bugs. However, every once in a while, a significant update is made available to make the experience "better", such as that on Windows Phone which recently introduced the ability to WhatsApp call, and send save and receive audio files as Android has always done (leaving Apple by its lonesome).., and the new Material Design for the Android interface which brought a fresh look to things (so they say).
These things make for an improved user experience, but if more similar features would be integrated throughout the app regardless of the OS platform, then one would truly say that WhatsApp is becoming better with version releases.
I hope this answer sheds some light.