I think it was unintentional but has played a crucial part in the game's appeal. When you get mana screwed, you feel the same emotional devastation as seeing the house win big in Blackjack. I think that low feeling drives players to try again and again.
Oh, I don't know about that. You really get used to how decks work. I've loset tournament games (Regionals and PTQs - though I never qualified :) to mana screw/flood and it didn't sting as much as when I made a stupid mistake that I immediately realised was a stupid mistake.
The problem with having to add lands to power up your deck for me is that it means I can't throw in the kitchen sink, as I'm wont to do if left to my own devices. A deck design must first of all work - and that's 50% getting the manabase down pat, which includes tough decisions (should I trim out a basic land for one more copy of OP sleeper rare I'm sure shreds the deck-to-beat to pieces? Hint: no). So you have to build a deck while respecting some constraints (minimum deck size, enough mana for your spells, sharp strategic focus etc). But that's like, all the fun in deckbuilding (which is all the fun in the game, for me :).
In fact, I know this will sound eminently silly but I believe that playing M:tG and in particular bulding decks has taught me important lessons that I took with me in my career as a programmer. The most important of which is: don't ever waste resources.
Perhaps a more esoteric lesson is this: you can still have infinite variety even without absolute freedom. Even with the burden of having to include land in your deck and risk mana screw/flood, you can still design any deck you want and have a lot of fun while at it.
