Weight: It's "heavy". If you are a big guy who needs the capacity of a Sea Lion, healthy and strong enough to river trip, you should be able to lift it to whatever height you want to. A smaller person will likely have a problem. 7/10
Tripping: The Seal lion is rated at about 400lb so my 6' 265 (at the time) body could get in and I figured for 100 lb of gear, Tent, food, pfd, paddle, 1st aid, etc. It all adds up even when you use backpacking stuff. I have packed for 5 days with some extra stuff for the group, and wasn't out of room. I bought new neoprene hatch covers for it (125) and everything stays dry. So packability and max carrying weight 10/10.
Comfort: The seat back, for me, was awful. At a well used 50 years old, after a hour it felt like I had been hit with a sledge in the spine. A high backband solved that problem and I have done 30+ mile days on the river. Its a bit close in the foot area. Crocs are out as footgear, Sandles will hang up on the nuts from the cleats holding the rigging. I intend to reverse the screws this winter. The knee braces got pulled out. I could not use them because they compacted my thighs. (pole climber) I brace against the coaming with no trouble though. 3 bolts solved the thigh brace problem. So, in original config 3/10. 50 bucks plus shipping later and pull the thigh braces, 8/10.
Stability: Like I said, its my first kayak. At first the round bottom made it a bit nerve wracking. Once I got used to it, straight and level is easy and smooth. Initial stability 10/10. Secondary, I have a lot of upper arm and shoulder weight so when she wants to go up on edge, I have to watch it because she wants to go quick. This seems to be a learning curve for me and with bracing and a little more thinking about hip placement, I can bring her back. She is much more pleasant when there is a little weight in the back, but no one wants to run loaded all the time. My daughter, who weighs a lot less than half of me, and is 8 inches shorter, has taken it out empty with no problem. Probably because she isn't as top heavy. So 6/10 for me YMMV.
Steerability: The rudder really helps with tracking in the wind, but it will go straight if you are doing your part in calm times. If you have to make hard turns quickly, you will work for it. She ain't a WW kayak. I have made it through some rough stuff, and also got to swim. I wont say it is all the kayaks fault though. I have just started to get up on edge for turns and that seems to help where the water isn't pushing. I do use the rudder to help on hard turns to get through rock features though. Hard to call this, but I am going with a 7/10 because I think it operates like designed, but I am doing stuff that it really wasn't designed for.
Speed: It would probably go faster if there was a younger guy paddling. I can take my son in short distances in his Carolina, but over the long haul, 16 is different than 50. Its fast enough for me. BTW, it will wake surf better than the kids boat.
So overall, if you are a bigger guy, who wants to try a kayak and do some kayak camping, it would be hard to beat a used Sea Lion. If you want to take the family to the lake, my daughter who weighs a lot less than me finds the Sea Lion a better fit because the hull is narrow. Makes it eaiser for her to paddle correctly.
Downsides - The inside of alum canoes is like a reflector oven. 2 cans of flat tan camo paint cured that. Seats are alum canoe seats. For long trips you need a backrest. Alum sticks on rocks, period. It will hang up where a plastic boat will bump over.
Nothing is a 10 but if you are looking for a tripping boat that you can bang up some and still plan on owning for a long time, you will have a hard time finding a much better, almost maintenance free, canoe that works this well.