I just love the idea of expanding the quest-mode to a full-blown Shandalar-like RPG! You guys are awesome! *thundering applause*
For me the most fun part of Forge is playing the Questmode. At the same time it's the part of the game that still can be expanded the most, mainly because it reminds me of good old Shandalar from way back in the day.
Because I don't know jack about programming all I can offer is a sort of "wish list" of features that would make the new adventure mode both as fun and as motivating as possible:
1. Stay close to the Magic Universe and metagame. We all know that MtG is really just a bit of cardboard, but thanks to the power of imagination it conjures up epic battles with daemons, dragons, gigantic beasts and everything else the fantasy genre has to offer. That is part of what makes the game fun. Plus the metagame of the players being dueling Über-wizards, not bound to any one plane of existence is as epic as you can get. Tap into this reserve of awesomeness that the planeswalker concept is.
Speaking of planeswalkers, over the last few years WotC has explored and expanded the mythology surrounding the planeswalkers both in terms of game play (the planeswalker cards) and beyond (books, comics, more on the whole multiverse idea). Wouldn't it be great to have an adventure as a planeswalker yourself? Traveling the multiverse and battling the powers that be? Hell yeah! Plus you could meet the other established planeswalkes, like Jace, Chandra or Garruk. Maybe you help them, work for them or fight with them. As long as it doesn't conflict with WotC's copyrights, of course.
2. Have a learning curve. Now I know that Forge is not meant as a tool for teaching MtG to newbies, but a learning curve is also a power curve. Ideally you would start off with few and only basic cards. Not terrible cards, but rather core-set cards, if you want the interesting cards you have to work for them. In term of game mechanics that would mean creating different cardpools for different game worlds. The starting world/plane/kingdom/city etc. would be offering the cards from Magic2010 and Magic2011. Combined with not too tough enemies it would allow players to create a first deck that is both basic and decent. The intricate stuff and complicated mechanics come later. The concept of having different cardpools is already an important part of Magic as a trading card game, just think of the different formats like block or standard. Every set and block is both build along certain themes and mechanics that create synergies. Including those in the new quest mode just seems natural. You want an artifact deck? Travel to Mirrodin and earn yourself some cards from the Mirrodin block!
3. Loot. Everybody loves loot. The core of many a RPG is the hunt for loot. It's both fun and motivating. So loot should come in different varieties and with differing predictabilities. One thing that I feel is missing from the Quest mode is the possibility to by some new pre-constructed decks. Because very single card you get is random getting the proper cards, let's say for a millstone type of deck, is purely a matter of luck. Getting together 4 copies of the cheap "
Tome Scour" took me more than 100 games. Being able to earn or buy preconstructed decks, even if they are very weak, would not only eliminate the problem of having to amass a huge cardpool until you can build more specialized types of decks, it could also be an incentive to try out a new type of deck after earning a whole deck by finishing a quest.
Other loot besides cards is already a part of the Questmode: the pets, the lifepoints and the adventuring gear. There's no good reason to not expand on that part of the game. So more pets, more pet slots, more stuff and why not also as a quest reward?
4. Quests. From catching rats to slaying Gods. In the current version of Forge the themed quest battles are great fun. Theming the opposing decks just adds a lot of fun to the games. I would like to see more of that! Ideally story-driven multi-part quests with different routes to take. Also the quest rewards should reflect what you have just done. Searched an abandoned mine? You get some cards relating to crystals and gemstones, depending on the difficulty anything from crystal rod to one of the moxes. You just helped an evil cult to take over a city? Add some new black clerics to your decklist.
5. Special game modes and play conditions. To keep a game interesting it's nice if you can shake up the rules a little. Maybe some special conditions or restrictions in deckbuilding. So there a quest were you can only have green cards in your deck, or only single copies of cards, or at least 200 cards, or cards of every color etc. (essentially recreating some of the fun formats, like Singleton, EDH or Stairwell) There should also be a "Duel Mode", that cancels all your advantages and disadvantages to set the conditions of the classic MtG game: 20 life, no free mulligan and nothing on the board for you and your opponent. Just to keep that old MtG-feeling alive.
Or steal some ideas from the planechase cards and some permanent effects to a game, if you are in certain places or planes.
Llanowar, for example, makes every creature on the battlefield a mana-producer. Unshakable effects like this (good or bad) mix up the gameplay, forces players to new tactics and can also add more flavor to the game.
For an extra level of awesome add some form of limited format (sealed, draft, etc.) to the quest-mode. I have no idea how, but would be tremendous fun. Plus you only get to keep the cards if you win. Now that would be an incentive to win.