It was an impressive proof of concept. There are technically better cryptocurrencies (along pretty much any dimension), but they just didn't get as much attention. Maybe these articles about how bad bitcoin is should call out some alternatives.
The Lightning network is an overloy network on Bitcoin that allows faster transactions and higher transactions-per-second. Due to the economics of mining, it won't decrease the overall electricity usage of the network, but will make it more "efficient" per-transaction.
Ethereum is more programmable, to the point of being quite easy to shoot oneself in the foot. (Bitcoin is intentionally not Turing-complete to avoid abuse.)
Anything with proof-of-stake instead of proof-of-work is going to be less wasteful in terms of electricity. Ethereum is trying to get there but it has been delayed a lot.
The slow pace of block creation has been a problem with Bitcoin for a long time and lots of blockchains have higher transaction-per-second capacities and quicker verification times. Ripple was promising but had some serious scandals and I don't know if it has a future. Anyway, Bitcoin is one of the slowest ones out there now.
Several have improved on the privacy/anonymity aspects. The most famous of those I think is Monero.
(I did not want to sound like I was advocating for anything in particular, but since it would be on topic, and you kindly ask :)
As you said, as a start, anything with a higher TPS (transactions per second) is more efficient, which helps. Some notables, in my mind (not exclusive, of course) ...
I really love what Cartesi is doing: They are bringing Smart Contracts to the "linux stack", securely (same guarantees than on-chain) but -outside- of chain. This will, obviously, raise efficiencies ...
The Fantom chain is high performance -and- their contracts are Ethereum-compatible (smart!), aside from it being a very nice, well thought out "ecosystem"
The NANO token makes it a point of pride, exactly how -much- more efficient ("Eco-friendly") it is than BTC, and their approach is interesting. (It has got some HN love lately and everything :)
(On a tangent, I am also a fan of what FRAX is doing in the stablecoin space, bringing decentralization and transparency to that space ("Frax is the world’s first fractional-algorithmic stablecoin") ...