That's pretty much all it does: exposes Hubitat devices to Alexa. Beyond that, you can also query some devices (e.g., "What is the temperature of XYZ Sensor?"). I'm not trying to make it sound boring; this is about what the SmartThings integration does, too, and it's probably how most Alexa integrations with other platforms work. It is not two-way: it doesn't expose other devices on Alexa to Hubitat, nor does it expose the Alexa device itself to Hubitat.
Yes, but you'll need something beyond Hubitat's built-in Alexa Skill integration. The only "official" starting point here would be an Alexa Routine. You should already be able to use these with SmartThings-exposed devices. The automations you can create with Alexa Routines are not as flexible as those you can create in Hubitat (or SmartThings), but you can make an Alexa device speak as part of the actions in your routine. Amazon does not have an official "TTS" API for their devices, so Hubitat is not able to make Alexa speak natively.
But that hasn't stopped some community members from figuring things out. 
The Alexa TTS and Echo Speaks 4 integrations are probably the most popular; you may remember earlier versions of that last one from SmartThings. The landscape should really be similar over there; this isn't a Hubitat-specific limitation. For Google devices, Hubitat has a built-in Chromecast integration that should work Google Home devices natively. It's still technically in beta, and people have mixed luck, but it's there. With either of these options, you'd be able to do the entirety of the automation on the Hubitat side, giving you more flexibility, but at the cost of some un-official-ness.
