If you're going for the HomePod (vs. the HomePod mini), buy it only if you have Apple Music or iTunes Match. It's really not worth it otherwise. I have a Google Home, Google Home mini, and an Echo Dot (got all of them for free except the HomePods).

Assistant wise, you'd get better results from Google Assistant/Alexa. Apple has been lagging and playing catchup (from not having multiple timers in the initial HomePod release to adding voice recognition last year when Google had it earlier). The answers are more limited like your iOS Siri (don't expect anything better). Even worse, it seems like HomePod's Siri backend is different than say an iPad's which generally means it's a generation behind. For instance, the HomePod doesn't really support continuous conversations/follow-up questions.

Siri is ok finding popular music, but if you ask it to play the "The A-List: K-Pop playlist" vs. "The A-List: Pop Music" for instance, it's a tossup on which it chooses dependent on the alignment of the planets. The same goes for musician names where if it kinda sounds like the more popular musician, it will tend to choose the more popular one. Furthermore, if you have a specific version of a song (say acoustic/live version), then the HomePod always tends to pick the most popular version of the song even if you say "acoustic" or any other hints.

There are "Shortcuts" on the HomePod. You can use it to add Todos to third party apps (if you don't want to use the Apple Reminders integration) or play a podcast from a third party player from your iPhone/iPad. Not as useful as Alexa skills and every now and then it takes some magical phrase to correctly activate them. The main problem with Siri beyond lacking knowledge is that Siri lacks consistency. While it's ambitious in letting you say anything versus the narrower "scripted keywords" that Alexa understands, if you say something one day that it perfectly understands and repeated it exactly a week later, you have no idea if Siri will still understand you. I read about this complaint before against Siri, but having experienced it more than a few times now, it is incredibly frustrating. And Siri sometimes (unintentionally) mocks you by repeating all the main parts of your request back to you correctly, but it does the wrong thing.

Hardware wise, the HomePod sounds better than a Google Home, Google Home mini, and Echo Dot. But of course, the others are cheaper. Two HomePods do sound better than one. Besides the better output, the mics are significantly more sensitive even in a loud environment. If you're putting the HomePod in a noisy kitchen or playing music loudly, then a HomePod can pick up your voice without you shouting at it.

The Apple TV integration has gotten better, but even with two HomePods, a relatively cheap home theater setup sounds better and can be used for all your TV content instead of just from your Apple devices. If you place the HomePods right next to the TV at roughly the same height, they sound good but if you move them too low/high or around the room, it does sound "off". The whole spatial two HomePod thing kinda does work for music in a room, but for TV content, it does not.

Really the other assistants are as good if not better than the HomePod, then the only distinguishing (non-privacy) feature is if you want a premium and pretty good way to listen to Apple Music. Maybe a few more music services which hopefully will be available soon. I don't regret buying the HomePods at all because I do like listening to music on them, but all of the assistant and "smart" tech is available on your iPhone if it can hear you.