For years I've been telling people, in person and on my web site (findascope dot com), that you simply cannot buy a decent, minimal telescope for under $100- and then Celestron came out with the 21024. This is the first telescope I've seen that's so cheap anyone can afford it- and yet will still deliver decent views of the heavens. The Dobsonian-type mount is sturdy and vibration free, unlike many shaky mounts seen on telescopes costing 2x or even 10x what the 21024 delivers. Optical quality is good, and with a 3" mirror it should deliver usable images up to a magnification of 150x in good conditions, using the 50x per inch rule.
With a focal length of 300mm, the supplied eyepieces will provide magnifications of 300mm/20mm = 15x and 300/4 = 75x. You'll find that for most uses the 20mm eyepiece is actually more useful, as many of the most interesting objects in the night sky- galaxies, nebula, and star clusters- are quite large. For viewing the planets you'll want to use higher power- either the supplied 4mm eyepiece, or perhaps (as one reviewer suggested) a better "Plossl" type eyepiece from Celestron or another supplier. A 2x Barlow lens will double the magnification available from the supplied eyepieces, but maximum magnification isn't always useable. Buying better eyepieces is always a good way to spend your astronomy dollars, as you can use them when you move up to a larger telescope.
You'll also want a good guide to the night sky. My favorite is a book entitled Turn Left at Orion: A Hundred Night Sky Objects to See in a Small Telescope--and How to Find Them
. It's intended for owners of small scopes, and will teach you to navigate the night sky by hopping from object to object.