>3.>>Does your GPS show detailed view of riverbanks, density of forest, hills?This has less to do with "GPS" as a system, and more to do with the receiver and mapset you choose. Some are more capable than others.
Older models like the GPS12 in
>>465872 don't offer any mapping - they'll show waypoints on the screen and a tracklog.
Some lower-end models give you limited internal memory for maps (couple hundred MB, for the eTrex line).
Personally, I'd bump up to something with a memory card. That'll allow you to install huge maps, and switch between them using multiple memory cards if you so desire.
Some newer/more expensive receivers let you throw raster images onto the map screen as an overlay (scanned trail maps or aerial photos, for example). Garmin calls this "Birds Eye". It's a fairly new feature.
Pic is 3 different mapsets from the same position. There's also maps available for marine use. You could build your own if you want. There's also free stuff available online, though the quality and coverage is hit-or-miss.
The name-brand stuff is going to be consistent over the entire area covered by the mapset (CityNav covers US, Canada, Mexico).