Gears
Amazing art design, let down by terrible graphics. Great music that serves to enhance an ambitious and rewarding narrative among the absolute best in gaming. Decent gameplay, hampered by half baked mech battles and a broken random encounter system that lets you move around after a battle has been triggered, but before it actually starts.
For example, you will walk up to doors and not be able to go through, because you have triggered a fight and don't realize it. This won't be a major annoyance until Babel, where it will happen during forced platforming sections and the battle will load while you're in mid air, then you will fall after the fight.
Cross
Great art design, served well by gorgeous graphics. Unrivaled music that serves a unique and interesting story. Decent gameplay, hampered by a somewhat forced element based system. A follow up to Chrono Trigger that is more Earthsea than Lord of the Rings in approach. Meaning it is not a straight continuation, but more experimental.
Both are worth playing, but I think Cross holds up better in graphics and gameplay. However you may be more satisfied by Gears.