It was far more interesting to collect the full set in the first game. The game encouraged this, with the soul gem previews and the explicit elemental bonus given for having multiple characters of the same element. Even the way the Skylanders were presented in the collection screen encouraged a full set.
Giants just dumps all figures into one scrolling screen. You can't see what you are missing. There are no soul gem previews for anything beyond the eight new figures. Hell, the game can't even count how many you have correctly. It also counts the series 1 items as "Skylanders", but not the series 2 items, so your count is never accurate. There are so many variants that collecting everything is an absurd idea. Buying the occasional Legendary or Blue figure for the first game was fine, but right out the gate, Giants had triplicates of many characters (regular, legendary, lightcore), not to mention the other day one variants like Rock Zook et al.
I have been considering what I will do with all these figures in the future. There is a lot of sentimental value in the initial collection from the first game. That game was very well written and designed. The total number of figures toed the line but didn't go overboard. I feel overall, it is one of the best games of that generation. I would be proud to someday watch my daughter play the game with her child, along with the other greats from previous generations.
Conversely, Giants felt rushed. The writing is poor and there is much less of it. Despite the game clearly being targeted at those who had played the first, The first quarter of the game is spent rehashing how to push buttons, aim laser beams, and play Skystones. The tutorial effective consumes a quarter of the full game. They allow you to use the adventure packs from the first game, but made almost no changes to them, and didn't even bother giving a thematic reason for them to exist as in the first game. No cool pirate ships sailing in, or dragon horn to blow. Instead, a wall of text appears when you place the adventure item on the portal, and you simply teleport there.
I understand that they probably only had eight months or so to complete the game, but it should have just been delayed a year and fleshed out better. Nightmare mode is more frustrating than challenging. The Giants are simply slower Skylanders that can break walls. While I have enjoyed the game, overall it feels cheap to me, and I won't care if it never gets played again. I'll probably sell off all the Giants related figures this fall, and keep the original set forever. It will be kind of funny to have this sort of thing be a family heirloom.