How much can I get out of the World Of Warcraft Starter Edition?

The short answer is no. The game has a level cap of 100 (assuming you have all expansions), so you'd get 20% of the total leveling experience and none of the post-game (what you do when you hit level cap) content.

The starter pack is roughly analogous to a demo in a singleplayer game in that regard; it gives you enough of the game to understand whether or not it's something you'd want to spend money on.

The long answer...

You can sink a lot of time into a level 20 character, even with the restrictions imposed upon a starter edition account. One of the most common ways to do this is in PvP battlegrounds.

For some people (including myself), the fun in this is finding ways to explore the world or optimize your character within the starter edition restrictions. You can still do the following in the starter edition:

• Level professions up to rank 100
• Run level 10-20 dungeons solo, or with up to 5 people (although there are only a few, so these can quickly get boring).
• Complete all quests available to your faction from level 1-20
• Collect companions and toys (obviously, a lot of these are not available to a level 20, but there are still loads to collect).
• Participate in yearly world events like Brewfest(Oktoberfest), Midsummer Fire Festival(Summer Solstice), and Hallow's End(Halloween). While not all content will be available for a level 20, there is almost always something to do for everyone.
• Visit the Darkmoon Faire. The carnival comes to town for the first week of every month. There are quests, gear, and toys exclusive to this event.
• Explore! There are very few barriers in the game that will not allow you to enter due to not having the latest expansion. The only risk in traveling is that most areas are dangerous to a low-level player (but don't let that stop you).
• PvP Battlegrounds: Once you hit level 20, you are matchmade against allies and opponents levels 20-24, but all players levels are scaled to 24 to compensate for hit chance/base stat disadvantages. You can use online databases like http://www.wowhead.com/ to find the best gear for a level 20 character. Cynwise has created a great guide, albeit outdated, for level 20 twinking https://greentintedgoggles.wordpress.com/2011/07/26/a-guide-to-trial-account-twinking/.

If you're up for a big time sink, and a bit of a challenge, you can play WoW for quite a while at level 20. And if you're getting a little bored, you can always start over from level 1 with a new class!

One of my level 20 characters, in case you are interested: http://us.battle.net/wow/en/character/Auchindoun/Creativity/simple