Man.. I haven't been playing MTG for a bit, I did play a kaladesh pre-release, and it was great, but the spoilers on this set make me think the limited environment will be fun again. There's only a few cards that look standard viable, but a bunch of them seem like lots of fun stuff for limited. All the value spells that are too slow for standard, or the synergistic stuff that isn't bad on it's own, but may not be powerful enough to build around for standard..
Talking about things like Glint-sieve Siphoner , Rishkar's expertise, Siege modification, Greenbelt rampager, etc..
Speaking of Rishkar's expertise, all of the expertise 'cast a spell X or less for free' spells look very playable in the right deck for standard. For example, Sram's Expertise is 2WW for three 1/1 servos and cast a 3 mana spell for free. You are basically paying 1 mana for three 1/1s then, which is amazing. You can cast something that you might not have the right color mana for, too. The flexibility and tempo of all those spells seem great. Rishkar's Expertise is a big value spell, and it's definitely powerful. It will just depend if a midrange/control deck can run green and decent sized creatures. Imagine running a G/B controllish deck, with a creature out, let's say Kalitas for maximum lulz. You go Rishkar's, into Yahenni's Expertise, into Liliana, the Last hope. Possibly using her +1 to finish off something that had 4 toughness to survive Yahenni's. You draw 3+ cards, clear the board, get a bunch of 2/2s, and play a planeswalker in the same turn. Yikes. That's cruel ultimatum level of power. Sure, it's not all in one card, but you are drawing a bunch to refill.
Combining any of the expertise spells into a 'cascade' style play is going to be very powerful. Or, if the mana is good enough for 4 colors, Rishkar's into Dark Intimation, especially if there is a Bolas card in this set. There's all kinds of crazy plays that can be made with those spells. If the red or blue one is 5 mana, cast 4 or less for free, then there is some ridiculous possibilities for chaining 3 of them together.