Sorry it will be a long post, but that pretty much sums up all my improvements list for SE. I'll put a (*) symbol next to the ones I personally find more urgent/useful.

Gameplay

When rapidly selected, cards might freeze oddly onto the board
*Add the possibility to inspect opponent's cards during their turn
Add interactive keywords (like pop-up windows) instead of putting explanation into brackets: I know, it means many cards from every set will have to be redesigned
*Add a counter for abilities with duration
Do not show a card until it's actually put into play (it's very annoying sometimes) or takes effect

Campaign screen and menu

The buttons below (deck, merchant, multiplayer) are pointless because they are repeated in the menu
The Resume button should be placed at the top, not the bottom
Add options for graphics like fog, detail level, and so on
Help section: card info and game rules should be swapped
Help section: card info: top left: "energy" is mentioned instead of "resources"
Help section: card info: bottom left: distinction between claw, sword, fire, ice, electrical and arcane damage should be mentioned
*Help section: card info: card types (hero, ally, ability, item, location) as well as subtypes should be listed here
Help section: game rules: sacrifice: it should be pointed out that every card you sacrifice piles up and is available at the beginning of every turn
Help section: game rules: target: the camera no longer moves to your opponent actually
Help section: game rules: finished: it should be pointed out that your allies are readied at the end of each of your turns
Help section: game rules: it should be pointed out that all abilities on a card cease to have effect once that card leaves play (for example, Necromancer's Shroud or Aural Battery)
Help section: game rules: hero abilities: the hero has no longer a purple background if its ability can be activated
Help section: game rules: key terms should be placed under card info instead of game rules
*Help section: game rules: key terms: other terms like hidden, frozen, poisoned, disabled, exiled, duration, sustain, exhausted, readied should be added

Multiplayer

*Last games section (both rated, unrated and meltdown) should show the last 50 games, according to the new best score system

Merchant
*Add the new filter from the deckbuilder instead of the old one

Other suggestions

While waiting for battle, one of the suggestions mentions "ongoing" effects, even though they are now called passive abilities
It would be nice to have a "Balor clock and calendar" (always visible on the campaign screen) and seasons going accordingly
*Add a player profile page (not a window) where all stats are shown
*Add a player research bar, a friend list and a private/group chat (also, chat should be visible on merchant and deckbuilder screen)
*On the Android version, whenever I have to write something (login, in-game chat, card or player search) that thing is shown white or just too pale grey, very hard to see
*Add the possibility to filter cards by typing words from their ability (heal, draw, return, exile, discard, tribes etc)