In my defense, the Red box has an EXCELLENT DM GUIDE WITH monsters or a mini monster guide, a grid, and monster tokens for half the price of Monster Vault.
It will ONLY get you up to around level 5, even with Heroes of the Fallen Lands however, with you making up adventures and adding in monsters. For the DM Guide in it, and the monsters however, it's actually not a bad value.
Monster Vault is a better source overall, and you get up to level 30. However if someone is only wanting to try it out, it's two times the cost of the Red Box. Red Box is merely the cheaper option for someone just trying it out, and has some DM stuff the Monster Vault doesn't have. Monster Vault is better, but some may feel wronged by it if they spend the extra $20 only to find they don't like the system.
Which is to say, $40 investment of HofL + Red Box
vs. HoFL + Monster Vault = $60
In which case I'd probably start looking at getting a core rule book set from Amazon which is $66.
Just my two cents and why I put in the Red Box as one of the options.