Learn Icelandic: Mig langar ekki í viðhaldsmikinn húsbíl. - I do not want a high-maintenance campervan.

It is a compound of viðhald (maintenance) and the adjective suffix -mikill (great or much), joined by the genitive -s-. Adding -mikill to a noun creates an adjective describing an abundance of that thing, so viðhaldsmikill means maintenance-heavy or high-maintenance.

Why does the adjective end in -mikinn rather than -mikill in this sentence?

It is modifying húsbíl (campervan), which is a masculine noun in the accusative case here. The masculine accusative singular form of -mikill is -mikinn, just as -lítill becomes -lítinn.

Why do we need the preposition í after langa ekki?

When the verb langa (to want) is followed directly by a noun, it always requires the preposition í. If you wanted to express doing an action instead, you would use að followed by an infinitive verb, such as Mig langar ekki að kaupa... (I do not want to buy...).

Why does this sentence start with Mig instead of Ég?