I like a handful of these.
Celerity is interesting, for example. When I read MaRo's article and saw that they almost named "haste" that, I really wished they had. I think that playable at instant speed is a good mechanic for the name. My one reservation is that it occurs so seldom that it may not be worth keywording.
I like the principle behind Landheart and Weakness. I don't think, however, that they should be keyworded. I like that people are thinking about how to take advantage of what land types peole control and what colours their creatures are and such, but I think there should be more flexibility in how those things apply than one set of bonuses or penalties. For examples of some cards I've designed that have similar traits, see Marsh Goshawk, Arboreal Glider, Frozen Spirit, and Torpid Spirit in the
Blue Master List.
I like the idea of Venom. In fact, that very topic came up just a few days ago. The objection was raised (and it's a good objection) that there are three abilities that are very similar and which are often associated with venom: creatures die when blocking/blocked; creatures die when damaged; creatures don't untap next turn. All three exist and are actively used ([card]Serpentine Basilisk[/card], [card]Tangle Asp[/card], [card]Orochi Ranger[/card])
Hesitation seems kind of interesting. Mechanically, I'm not absolutely positive how you would word it, but anything that allows for undercosted fat is neat, in my eyes.
Essence can probably just be Spirit Link, instead, with the standard "whenever this creature deals damage" trigger. I'm pretty sure that a lot of people are expecting that ability to be keyworded pretty soon anyhow.
Peek would be okay, if instead it were "Peek X" and allowed you to rearrange the top X cards of your library. Otherwise, it falls into the same rut as Threshold -- that they might want to bring Threshold back with some value besides 7 as the magic number, but would have to rework the mechanic to do so.
Recover, Autoresolve, Psion, Repulse, and Force all seem incredibly narrow. They hardly ever appear and when they do, they're better off leaving the details of the mechanic unfixed. For example, something like Sparksmith is a perfectly good direct damage creature, but it doesn't fit the Psion template. Force locks out the possibility of other alternate casting costs, which is really the one area that can be tampered with to make an ACC spell more or less powerful