The Necron codex is a really well designed book in my opinion, mixing some real combat choices with a backbone of shooty units that are reasonably priced.
Whether you want to go hordes of implacable Warriors, the more elite strike force of Immortals or the mindless swarms of Spyders, Scarabs and Wraiths you’ll always have plenty of tools for the job.
My favourite idea is the Crypteks and Lords, with the ability to split off and join other units, adding utility, flexibility or synergy. Why wasn’t the Eldar codex designed like this with the Farseers and Warlocks!
Some of the choices are more expensive, like Lords with Rez Orbs, but others are much more reasonable…
A list I came up with and thought might be interesting was the following:
5 Warriors (Night Scythe) x 2
10 Immortals (Gaus) x 2
10 Immortals (Tesla – or maybe Gaus) x 1
O Lord, Scythe, ROrb x 2
5 HoDestr (Eld Lance) x 2
= 1450 points
The 10 HoDestr (with Lances) would be put into each troop squad, two in each. The OLords would go with the Gaus Immortals.
For a 1750 point list you have 300 spare points, ideally I would want two Doomsday Arks, so would need to trim some points, but even three more Scythes as transports could work (not all squads would start embarked).
You end up with the warrior squads as objective sitters, the Scythes as anti air/harassment units, plenty of firepower on the gaus/telsa Immortals with each squad putting out two lances shots. The gaus squads who need to get in close and personal also will have Rez Orbs making them about as survivable as terminators. (Assuming they get their 3+.)
It’s a relatively simple list, not requiring a huge number of vehicles or troops. Putting some points aside to beef up the OLords, maybe with Mind Shackle Scarabs and Sempiternal Weave would also make the Immortal squads a bit scarier in combat and let the OLord absorb some damage as well as really dish it out. Unfortunately the weakness is the lack of fearless or stubborn and instant death template weapons which don’t allow reanimation protocols.