You enjoyed the story, the voice-acting, the puzzles, the 'aha' moments, and you thought co-op was brilliant. You even started playing it a second time, getting extra achievements, but as epic as it might've been, the experience was wearing off a bit.
Now would be a great time, then, to visit thinkingwithportals.com to get some new Single Player or Co-op maps to bring back those joyful experiences (well, at least the puzzle solving and aha moment ones) :)
A friend and I downloading some of the co-op maps with 4 or 5 stars and found some of them very challenging (good luck finishing the 'Turret Love' level, for example).
How to install levels
I'm not an expert at this yet, but once you've downloaded and extracted the maps you want to try, there are two places you can place the levels, based on their file extension.
Go to ...\Steam\steamapps\common\portal 2\portal2\
Files with a *.bsp extension go into the 'maps' folder (keep a note of the filename somewhere - i.e. in a Steam chat so you can bring it up in game)
Files with a *.vpk extension go into a folder called 'addons' (which you probably have to create) (i.e. common\portal 2\portal2\addons\*.vpk)
If there are other files, then these are likely the source files that you can open and edit with the Hammer editor (see Steam Tools, where you can download Dedicated Server apps to find it).
How to load the levels
If there's a ReadMe file included with your downloads, it's best to read through them quickly, but the general procedure is as follows.
Restart Portal 2 if it was already running (it checks for files when you start it).
Go to Options and find the setting to enable the Console, and bind a key to show/hide it. I have it bound to my ` key (above the TAB key).
For single player levels, at the main menu (or anywhere, really), press the 1 key to open the console, then type map NameOfLevel (i.e. map sp_interception)
For Co-op levels, you must invite a friend and wait until you are in the lobby area before attempting to change level (you could probably load the level in single player, but you'd never be able to finish it).
1. Press the ` key to open the console
2. Start typing - the console will auto-suggest commands and level names as you type:
changelevel [NameOfFile] - for example: changelevel mp_coop_duality
The console will show a bunch of output, maybe even some errors, but if both players have the files, it *should* load the level without issue. On some occasions my friend was dumped back at the main menu, and I was told he disconnected - not sure what the go was there, but we had plenty of other levels to keep us busy.
Feel free to discuss any good levels you find or arrange co-op sessions with other TDUCk members.
Here's a level a friend and I did yesterday (it's not us playing - I just did a YouTube search):
(Don't watch if you want to try this and doint want any spoilers)
I will be trying some more out tonight (~11am BST) if anyone's interested.